An invention according to Japanese Utility Model Application Laid-Open No. 64-53075 discloses an easily unsealable package that is easily unsealable, as described herebelow.
With reference to FIGS. 5(a) and 5(b), an easily unsealable package 200 is formed in the following manner. A laminated film 210 is arcuately bent into a tubular shape, and a film overlap portion is formed by arranging both-side arcuate lateral edge portions 210a and 210b thereof to overlap with one another. Then, the lateral edge portion 210a, which is a band-like non-seal portion and which is used as a pinch portion, is formed in a lateral edge portion on an outer surface side. In this state, two longitudinal seal portions 201 and 201 formed of a plurality of easily unsealable seals are formed substantially in parallel to each other, thereby to form a tubular package. Thereafter, one of two opening portions located in upper and lower portions of the package is sealed along the direction perpendicular to the direction of a longitudinal seal portion, thereby to form a lateral horizontal seal portion 202. Then, a viscous liquid, such as a tubular pasty food item, is filled into the interior of the package from the remaining opening portion of the package, and then remaining of the package is sealed, thereby to form the lateral seal portions 202 and 203.
The laminated film 210 thus used for the package is formed using a tri-laminated film, in which a drawn polypropylene is used for an outer layer 211, polyethylene is used for an intermediate layer 212, and an ethylene-vinylacetate copolymer is used for an inner layer 213. By use of the easily unsealable seals, the longitudinal seal portions 201 and the lateral seal portions 202 and 203 are provided to have the seal strengths of 1.0 to 2.6 (kg/15 mm). The package can be unsealed in the manner that the lateral edge portion 210a on the outer surface side is pinched by fingers and pulled.
The package disclosed in Patent Document 1 has problems. More specifically, in the easily unsealable package disclosed in Patent Document 1, surfaces of the drawn polypropylene of the outer layer and the ethylene-vinylacetate copolymer of the inner layer are thermally welded to each other. For this reason, a thermal welding temperature has to be set to be high in order to obtain a thermal weld strength to prevent tearing during, for example, transportation or usage of the package. As a consequence, a problem takes place in that since a separation strength is too high, it is difficult to obtain a predetermined easily unsealable seal strength. A second problem is that, because of thermal welding, the durability of components is reduced, and concurrently, the manner of processing leads to an increase of electric energy for obtaining heat. A third problem is that the tri-laminated film is expensive, so that there is introduced high costs of package materials themselves.
Japanese Patent Application Laid-Open (JP-A) No. 2004-43025 discloses a multilayered bag and a manufacturing method therefore and a bag-making, material-filling dual-structured bag. However, there are no descriptions regarding easily unsealable configuration of the multi-structured bag.
JP-A-2003-72001 discloses a laminated film and a package formed using the film. In the publication, there are descriptions regarding resin compositions of the film to achieve the easy-to-unseal property. However, there are neither descriptions regarding adaptation of the easy-to-unseal property to a material-filled package nor descriptions regarding researches and investigations on issues in the event of adaptation of the easy-to-unseal property to dual-structured bags.